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s390: always save and restore all registers on context switch
commitfbbd7f1a51
upstream. The switch_to() macro has an optimization to avoid saving and restoring register contents that aren't needed for kernel threads. There is however the possibility that a kernel thread execve's a user space program. In such a case the execve'd process can partially see the contents of the previous process, which shouldn't be allowed. To avoid this, simply always save and restore register contents on context switch. Fixes:fdb6d070ef
("switch_to: dont restore/save access & fpu regs for kernel threads") Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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@ -29,17 +29,16 @@ static inline void restore_access_regs(unsigned int *acrs)
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}
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#define switch_to(prev,next,last) do { \
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if (prev->mm) { \
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save_fpu_regs(); \
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save_access_regs(&prev->thread.acrs[0]); \
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save_ri_cb(prev->thread.ri_cb); \
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} \
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/* save_fpu_regs() sets the CIF_FPU flag, which enforces \
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* a restore of the floating point / vector registers as \
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* soon as the next task returns to user space \
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*/ \
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save_fpu_regs(); \
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save_access_regs(&prev->thread.acrs[0]); \
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save_ri_cb(prev->thread.ri_cb); \
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update_cr_regs(next); \
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if (next->mm) { \
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set_cpu_flag(CIF_FPU); \
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restore_access_regs(&next->thread.acrs[0]); \
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restore_ri_cb(next->thread.ri_cb, prev->thread.ri_cb); \
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} \
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restore_access_regs(&next->thread.acrs[0]); \
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restore_ri_cb(next->thread.ri_cb, prev->thread.ri_cb); \
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prev = __switch_to(prev,next); \
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} while (0)
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